1. Field of the Invention
This invention relates to an improved form of protective headgear arranged to protect the wearer against a hostile atmosopheric environment.
2. Description of the Prior Art
It is known to provide protective headgear in the form of a helmet including respiratory protective means to enable the wearer to work unharmed in a noxious or dangerous atmospheric environment. Arrangements of this general kind are described for example in U.S. Pat. Nos. 3,963,021 and 3,822,698 .
In a known form of respiratory protective helmet a helmet shell is spaced from a wearer's head to leave an interspace into which air is driven through a filter by a motor-driven fan situated at the rear of the helmet. The filtered air passes over the wearer's head and down in front of his face, being retained by a transparent visor. The rear edge of the visor and the rear portion of the helmet are sealed to the wearer's head by foam material extending between the visor side edges and the wearer's face.
It is also necessary to seal the airflow path existing over the top of the wearer's head. If such sealing is not provided then the air exiting from the filter escapes downwards around the sides and back of the head via the peripheral gap between the head and the rim of the helmet or hood. One known method of achieving this required sealing is to close the gap between the headband which is part of a harness assembly which supports the helmet on the head, and the helmet rim by means of an annular corrugated member of thin flexible and air impermeable material. At this inner edge the annular sealing member is either impermeably attached to the headband or may be made integral with the headband. At its outer edge the annular sealing member is impermeably attached to the helmet rim by some suitable means.
The required airflow from the space between the head and the helmet into the space between the visor and face is achieved by leaving a gap in the forward area of the said annular member which gap is confined within the sealing means at the rear edges of the visor.
This method of achieving the required sealing of the helmet or hood to the head is liable to result in several serious disadvantages. The headband requires to be adjustable in circumference to accommodate the various sizes of heads and this headband size adjustment can only be located at the front of the headband within the confines of the gap in the annular sealing member. This is not a preferred position for the headband size adjustment because the front rim of the helmet and also the visor are then situated too far forward from the face with heads of small circumference, and situated too near to the face with heads of large circumference. The preferred position for the headband size adjustment is at the rear of the headband. Another disadvvantage of the annular sealing arrangement described above is that the annular member cannot change shape sufficiently to permit the required wide range of headband size adjustment. Yet another disadvantage of the described sealing arrangement is that the headband flexibility, in the radial direction, is reduced and the headband is not able to readily conform to the varying shapes of human heads. Discomfort and pressure points are thus produced.